A radio access system and a radio network (hereinafter, referred to as “Long Term Evolution: LTE” or “Evolved Universal Terrestrial Radio Access: EUTRA”) of cellular mobile communication have been discussed in a 3rd Generation Partnership Project (3GPP). In LTE, a base station device (base station) is also referred to as eNodeB (evolved NodeB), and a mobile station device (mobile station, terminal) is referred to as UE (User Equipment). LTE is a cellular communication system where a plurality of areas covered by the base station device are allocated in cells. A single base station device may manage a plurality of cells.
LTE corresponds to frequency division duplex (FDD) and time division duplex (TDD). LTE using the FDD system is referred to as FD-LTE or LTE FDD. TDD is a technique which performs frequency division multiplexing on an uplink signal and a downlink signal, enabling full duplex communication in at least two frequency bands. LTE using the TDD system is referred to as TD-LTE or LTE TDD. TDD is a technique which performs time division multiplexing on an uplink signal and a downlink signal, enabling full duplex communication in a single frequency band. The details of FD-LTE and TD-LTE are disclosed in NPL 1.
A base station can transmit, to a terminal, a reference signal (referred to as RS) which is a known signal between the base station and the terminal. In regards to the reference signal, a plurality of reference signals can be transmitted for various purposes, such as demodulation of signals or channels and reports of channel states. For example, a cell-specific reference signal is transmitted as a reference signal specific to a cell in all downlink subframes. For example, a UE-specific reference signal is transmitted as a reference signal specific to a terminal in a resource to which a data signal to the terminal is mapped. The details of the reference signal are disclosed in NPL 1.
In a communication system, a base station and a terminal can implement communication using control information. In particular, in the downlink of LTE, the base station can notify the terminal of the control information through control channels, such as a PDCCH (Physical Downlink Control Channel) and an EPDCCH (Enhanced Physical Downlink Control Channel). The PDCCH is transmitted in association with a cell-specific reference signal, and the EPDCCH is transmitted in association with a UE-specific reference signal. In the LTE of the related art, the PDCCH can be mapped to a common search space (CSS) which is a region specific to a cell and/or to a UE-specific search space (USS) which is a region specific to a terminal. The EPDCCH can be mapped only to the UE-specific search space. For this reason, for example, when transmitting the control channel using the common search space, the base station notifies of control information through the PDCCH. The details of the control channel are disclosed in NPL 2.